340 Heads?

Look closer. Your casting number should be 3418915 instead of 341891 unless you just missed a keystroke. To the best of my recollection the 68-70 340 heads had a casting number of 2531894.
The 915 heads with 2.02 valves were 70 only for the T/A and the 915 heads with 1.88 valves were 71-72 340 heads. The 73 340 heads had a casting number of 3671587

A lot of this information is out of the Mopar Chassis Guide which I would not recommend trying to get through life without. Ever!

Now here's my .02 cents. I would find out what they are for sure and sell them to the highest bidder. J-Heads will bring about a hundred bucks, X-Heads will bring about $250.00 and T/A heads will bring about a grand. There should be a date code on those heads somewhere.
Take the money from the sale and include what you would have spent for a valve job and buy a set of Iron Rams from Hughes. If it turns out you need valves springs and guides you'll be money ahead. For $850 bucks you get heads that out flow the J-X-T/A head as well as the Eddy. You get a 62cc chamber that'll raise your compression about a full point and then some too.
The site is down today for some reason but keep trying.
www.hughesengines.com/Index/products.php?browse=search&search=4675&partid=25428


For not a lot more than a Valve Job you can get a set of Iron Rams